It is desired that an image forming apparatus is capable of dealing with various recording mediums. Thus, some image forming apparatuses are provided with a primary transfer station, an intermediary transfer member, and a secondary transfer station. In operation, each apparatus forms a toner image on its image bearing member such as a photosensitive drum, and transfers the toner image onto the intermediary transfer member in the primary transfer station. Then, it transfers the toner image onto a sheet of recording medium from the intermediary transfer member.
Japanese Laid-open Patent Application 2004-29054 discloses an image forming apparatus having an upstream transfer roller and a downstream transfer roller which are provided to reduce the apparatus in the amount of electrical voltage to be applied to transfer a toner image from the intermediary transferring member to a sheet of recording medium, by making the transfer station, that is, the station in which a toner image is transferred from the intermediary transfer member onto a sheet of recording medium, wider in terms of the direction in which a sheet of recording medium is conveyed in the transfer station.
In the case of an image forming apparatus structured like the one disclosed in the abovementioned patent application, it is desired that the amount by which electric current flows through the downstream transferring member is made smaller than the amount by which electric current flows through the upstream transferring member, in order to prevent the problem that a sheet of recording medium fails to properly separate from an intermediary transferring member.
Japanese Laid-open Patent Application 2010-243553 discloses an image forming apparatus having a roller 41 and a plate 66, which are upstream and downstream transferring members, respectively. The roller 41 and plate 66 are used to transfer a toner image onto a sheet of recording medium from the intermediary transferring member of the apparatus. In the case of this image forming apparatus, for the sake of transfer efficiency, the electric current I1, which flows through the roller 41, or the upstream transferring member, is made smaller than the electric current I2, which flows through the plate 66, or the downstream transferring member.
In the case of the image forming apparatus disclosed in Japanese Laid-open Patent Application 2010-243553, however, a transfer power source for flowing electric current through the plate 66 is necessary in addition to the transfer power source for flowing electric current through the roller 41. That is, two transfer power sources are necessary, being therefore likely to lead to cost increase.